Grinding apparatus for fibrous material

ABSTRACT

Grinding device, more especially a disc refiner for the paper industry; a rotor and a stator arranged in a housing; the stator guided radially but non-rotatably relatively to the housing and displaceable axially relatively to the rotor; a hydraulic servomotor provided for the displacement of the stator; on the servomotor an adjustable device for limiting the displacement of the stator in the direction to the rotor; the pressure chamber of the servomotor which is intended for moving the stator away from the rotor is provided with an axially displaceable abutment piston; means are provided for adjusting and keeping constant a required position of the abutment piston; the position of the abutment piston limits the displacement of the main piston of the servomotor and in that way the displacement of the stator.

United States Patent [191 Kahmann May 14, 1974 [5 1 GRINDING APPARATUS FOR FIBROUS 3,717,308 2/1973 Reinhall 241/244 MATERIAL [75] Inventor: Albrecht Kahmann, Weingarten, f' Exam" 'er GranVme Custer Germany Assistant Examiner-Howard N. Goldberg Attorney, Agent, or Firm-Robert A. Ostmann; Austin [73] Assignee: Escher Wyss Gmbl-l, Ravensburg, P. D d

Germany [22] Filed: Sept. 14, 1972 [57] ABSTRACT [21] Appl. No.: 288,943 Grinding device, more especially a disc refiner for the paper industry; a rotor and a stator arranged in a housing; the stator guided radially but non-rotatably [30] Foreign Apphcauon Pnomy Data relatively to the housing and displaceable axially rela- Sept. l7, 1971 Germany 2l46548 tively to the rotor; a hydraulic servomotor p i d for the displacement of the stator; on the servomotor [52] US. Cl 241/37, 241/245, 241/259.2 an adjustable device for limiting the displacement of lilt- Cl. the Stator in the direction to the rotor; the pressure [58] new of Search 241/37 l chamber of the servomotor which is intended for mov- 241/259'2 259'3 ing the stator away from the rotor is provided with an axially displaceable abutment piston; means are pro- [56] References Cited vided for adjusting and keeping constant a required UNITED STATES PATENTS position of the abutment piston; the position of the 2,930,534 3/1960 Baxter 24l/259.1 X abutmentpiston limits the displacement of the main 2,947,485 8/1960 Woodruff.... 241/2592 X piston of the servomotor and in that way the displace- 2,97l,704 2/1961 Johansson 24l/259.l X t of th t t r 3,158,333 ll/l964 Asplund et al..... 24l/244 3,212,721 l0/l965 Asplund et al 24l/37 7 Claims, 5 Drawing Figures GRINDING APPARATUS FOR FIBROUS MATERIAL BACKGROUND OF THE INVENTION The invention relates to a grinding device, more especially a disc refiner for the paper industry, which grinding device comprises a housing, in the housing a rotor and a stator which is guided radially but nonrotatably in guideways relatively to the housing and is displaceable axially relatively to the rotor, a servomotor being provided for the displacement of the stator, which motor is connected on one side to the housing and on the other side to the stator and comprises a main piston displaceable hydraulically backwards and forwards between a first and a second pressure chamber of a cylinder, an adjustable arrangement being provided for limiting the movement of the stator in the direction towards the rotor to a desired working position.

Such grinding devices are used in the paper industry for preparing the stock to be processed in a paper machine. The pressures which are to be applied by the servomotors for the mutual adjustment and holding of the two grinding members, the stator relatively to the rotor, are very high. As a consequence, the adjustable devices for limiting the displacement of the stator to the actually required working position are quickly damaged, since they have hitherto been constructed as screws with accurate and fine threads. It is then necessary as a consequence to stop the grinding device.

Hence, with one known hydraulic servomotor, the working position of the stator is adjustable by means of a setting screw which forms a stop. With another servomotor, the cylinder can be displaced axially by screws. Yet again, with another device, the overall length of the connecting parts between the servomotor and the stator can be altered by screws.

SUMMARY OF THE INVENTION The invention has for its object to achieve a disruption-free operation and a longer effective life of the grinding device, also at high pressures.

According to the invention, this object is achieved by the fact that the second pressure chamber of the servomotor designed for displacing the stator away from the rotor is provided with an axially displaceable abutment piston, of which the side facing the main piston comprises an abutment surface and of which the other side in association with that end wall of the cylinder which is opposite to it, defines a sealed third pressure chamber in the said cylinder, means being provided for filling the third pressure chamber with a liquid and for maintaining the introduced quantity of the liquid in the pressure chamber.

BRIEF DESCRIPTION OF THE DRAWING Embodiments of the invention are hereinafter more fully described by reference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal section through a grinding device,

FIG. 2 is a longitudinal section through another embodiment,

FIG. 3 is a longitudinal section through yet another embodiment,

FIG. 4 is a longitudinal section of a servomotor to a larger scale,

FIG. 5 is a longitudinal section to a larger scale of another servomotor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The grinding device which is illustrated is a tandemdisc refiner. The device comprises a housing 1 having a first end cover 2 and a second end cover 3. A bearing block 4 and a stator disc 5 are fixed on the first end cover 2. A shaft 6 is mounted to be longitudinally displaceable relatively to the housing 1 in the bearing block 2 and this shaft is sealed off. At one end, the shaft 6 is connected so as to be longitudinally displaceable to a driving motor (not shown), while it carries at its other end a rotor 7. A second stator 8 is axially displaceable in the housing 1 relatively to the rotor 7. The stator 8 is connected to a cylindrical part 9 which is coaxial with the grinding device and which extends outwardly through a central opening 10 in the second end cover 3 of the housing 1. The part 9 is guided by means of arms 11 and bolts 12 on guideways 13, whereby the radial but non-rotatable guiding of the stator 8 in relation to the housing I is assured. Provided for the displacement of the stator 8 is a hydraulic servomotor 14, which is connected on one side by means of a cover 15 to the housing 1 and on the other side by means of the part 9 to the stator 8. The part 9 is connected fast to a main piston 16 of the servomotor 14 and forms the piston rod of the said motor 14. The main piston 16 is displaceable backwards and forwards hydraulically between a first and a second pressure chamber of a cylinder of the servomotor 14. The first of the pressure chambers, i.e. the chamber indicated at 17, is intended for the relative movement of the stator 8 towards the rotor 7, while the second chamber indicated at 18 is intended for moving the stator 8 away from the rotor 7.

Pipes l9 and 20 are provided for respectively filling the pressure chambers 17 and 18 with a liquid and emptying the liquid therefrom. The pressure chamber 18 of the servomotor 14 which is intended to displace the stator 8 in a direction away from the rotor 7 is provided with an axially displaceable abutment piston 21, of which the side facing the main piston 16 comprises an abutment surface 22, and of which the other side, in conjunction with that end wall 23 of the cylinder of the servomotor 14 which is facing the said other side of the abutment piston 21, defines a sealed-off third pressure chamber 24 in the cylinder. Means (not shown) are provided by which a liquid is able to fill the third pressure chamber 24 through the pipe 25 and for maintaining the introduced quantity of the liquid in the third pressure chamber 24.

In the drawing, the third pressure chamber 24 is filled with liquid and the quantity of the liquid which is introduced is maintained therein. A liquid is guided into the first pressure chamber 17 through the pipe 19. The main piston 16 is moved up into the bearing position and against the abutment surface 22 of the abutment piston 21. The movement of the stator 8 in the direction towards the rotor 7 is limited to a required working position by the abutment of 21 and 22. If the stator is to be adjusted to another working position, it is necessary for the quantity of the liquid filling the third pressure chamber 24 to be altered, i.e. more liquid must be introduced or liquid released and the actual quantity in the pressure chamber 24 must then again be maintained.

The hydraulic actuating arrangementlnot shown) associated with the pipes 19, and 25 is later explained.

As regards the grinding device according to FIG. 2, the cylinder of the servomotor in the part 9 is constructed as a cavity 26 which is coaxial with the part 9. A main piston 27 is fixed on a piston rod 28, which is connected by means of a cover 15 to the housing 1. That first pressure chamber of the servomotor which serves for moving the stator 8 in the direction towards the rotor 7 is indicated at 29, and the second pressure chamber, which effects reverse movement of stator 8, is indicated at 18. A third pressure chamber between an abutment piston 30 and an end wall 31 of the cylinder is indicated at 32 and, like the third pressure chamber 24 in FIG. 1, serves to limit the forward displace- .ment of the stator 8 in the directiontowards the rotor 7 to the required working position. Thefluid transfer passages for the three chambers of the servomotor are shown at 19', 20' and 25'.

With the grinding device according to FIG. 3, three servomotors 33 according to the invention are arranged on the guideways 13. More than three guideways can also be formed on the grinding device, for example, six such guideways, but only some of them, for example three, can be provided with servomotorsVThe motors are hydraulically connected in parallel.

A servomotor 33 on the one guideway 13 of FIG. 3 is shown in greater detail in FIG. 4. The guideway 13 is fixed on the end cover 3 of the housing of the grinding device. The bolt 12 is fixed on the arm 11. 34 represents balls and 35 represents Seeger rings of a displaceable mounting of the bolt 12 in the guideway 13. On that side of the arm l] remote from the guideway 13, the servomotor 33 is flanged coaxially of the guideway 13. A piston rod 36 extends from the servomotor 33 through the bolt 12, without contacting the latter, as far as the end cover 3, on which it is fixed. The first pressure chamber 37 is intended for the movement of the displaceable stator towards the rotor and the pressure chamber 38 defined in the second pressure chamber between the main piston and the abutment piston 39 for the movement of said stator away from the rotor.

Situated between the abutment piston 39 and the end wall 40 is the third pressure chamber 41 for limiting the advance of the stator up to the required working position. 42, 43 and 44 are openings or connections for pipes of a hydraulic operating installation.

A double motor according to the invention is shown in FIG. 5. It is possible to visualise this motor, for example, in place of the servomotor 33 in FIG. 4. its two cylinders 45 and 46 are defined by end walls 47, 48 and 48, 49, respectively. Fixed on a piston rod 50 are two main pistons 51 and 52. One second pressure chamber 57 of the servomotor, i.e. the chamber of the cylinder 45, is provided with a displaceable abutment piston 53, between which and the end wall 47 is defined a third pressure chamber 54. As with the servomotors already described, this third chamber 54 serves to limit the advancing of the displaceable stator up to the required working position. First pressure chambers 55 and 56 serve for the advance of the stator and the pressure chamber 57 defined in the second pressure chamber between the main piston 51 and the abutment piston 53 and the second pressure chamber 58 serve for the rearward displacement of the stator 9 relatively to the rotor. Indicated at 59, 60, 61, 62 and 63 are openings or connections for pipes of a hydraulic operating installation (not shown).

The not shown operating installation associated with the grinding device and the servomotor consists of known separate elements. The purposes of the operating installation are explained by the example shown in FIG. 1.

The operating installation ensures:

a. The forcing of the main piston 16 by means of pressure in the first pressure chamber 17 into the bearing position against the abutment surface 22 of the abutment piston 21. The pressure chamber 18 defined in the second pressure chamber between the main piston 16 and the abutment piston 21 is at this time relieved of pressure.

b. A rapid movement of the main piston 16 away from the bearing surface 22 by means of a quickly rising pressure in the pressure chamber 18. At this time, the first pressure chamber 17 is relieved of pressure and the abutment piston 21 remains in its position. The rapid retraction (i.e. the quick relieving of the grinding device) occurs in the event of a sudden overloading of the driving motor, as for example when a foreign body penetrates into one of the gaps between the stator 5 or 8 and the rotor 7. When the overload on the driving motor subsides, as a consequence of the resultant relieving of the grinding device, the main piston 16 is once again pushed back and applied with pressure in the bearing position against the stop surface 22. The driving motor is then once again under a load such as corresponds to the position of the abutment piston 21.

c. The adjusting and keeping constant the position, i.e. the spacing of the piston 21 from the wall 23. For this purpose, a quantity of the liquid is introduced into the third pressure chamber 24 and the loaded value of the pressure chamber 24 is kept constant. It is not only a locking of the introduced quantity in this third pressure chamber 24 which is sufficient for this purpose. For example, if the introduced quantity, under the pressure of the main piston 16 on the abutment piston 21, flows away into the pressure chamber 18 because of a leakage at the said piston 21, the size of the pressure chamber 24 is reduced, that is to say, the distance of the abutment piston 21 from the wall 23 becomes smaller. The initially filled value of the pressure chamber 24 must therefore, in such a case, be produced again by replenishment of the liquid into the third pressure chamber 24.

d. The altering of the position of the abutment piston 21. For this purpose, more liquid is supplied into the third pressure chamber 24 and the first pressure chamber 17 is relieved of pressure, or liquid is released from the third pressure chamber 24 while the first pressure chamber 17 is under pressure load. The alteration is effected in dependence on an overloading or underloading of the driving motor of the grinding device, which lasts for a relatively long time.

I claim:

1. In a grinding device of the type including a housing containing a stator disc which is guided for axial movement toward and away from a cooperating rotor disc with which it defines a grinding gap, and a doubleacting hydraulic servomotor for shifting the stator disc and including a cylinder element containing a piston element which divides the cylinder element into a pair of opposed working spaces, one of said elements being connected with the stator disc, the other element being connected with the housing, and the servomotor being effective to shift the stator disc so as to decrease the width of said gap under the action of pressure in the first working space and to increase the width of said gap under the action of pressure in the second working space, the improvement comprising a reciprocable stop piston located in the cylinder element and defining therewith a sealed control chamber, the stop piston having one end surface which faces the second working space and is arranged to abut the servomotor piston element, and an opposite end surface which faces the control chamber; and transfer passage means through which liquid is introduced into and withdrawn from the control chamber.

2. A grinding device as defined in claim 1 in which said one element of the servomotor is connected with the stator disc through a cylindrical part which is coaxial with both the stator disc and the housing and projects from the housing through a central opening in a wall thereof.

3. A grinding device as defined in claim 2 in which the servomotor is coaxial with said cylindrical part; the piston element is connected with the cylindrical part; and the cylinder element is connected with the housing.

4. A grinding device as defined in claim 2 in which the servomotor is coaxial with said cylindrical part; the piston element is connected with the housing; and the cylinder element is connected with the cylindrical part.

5. A grinding device as defined in claim 2 which includes a plurality of said servomotors arranged parallel with and spaced around the axis of the cylindrical part, each servomotor being provided with said stop piston, control chamber and transfer passage means, and said one element of each servomotor being connected with the cylindrical part.

6. A grinding device as defined in claim 5 including a set of means for guiding the stator disc for said axial movement, each means of the set being coaxial with one of the servomotors and comprising a stationary member connected with the housing and cooperating moveable member which is connected with the cylindrical part through a common connection which also serves to join that part to said one element of the associated servomotor.

7. A grinding device as defined in claim 6 in which the piston elements of the servomotors are connected with the housing and the cylinder elements are connected with the cylindrical part. 

1. In a grinding device of the type including a housing containing a stator disc which is guided for axial movement toward and away from a cooperating rotor disc with which it defines a grinding gap, and a double-acting hydraulic servomotor for shifting the stator disc and including a cylinder element containing a piston element which divides the cylinder element into a pair of opposed working spaces, one of said elements being connected with the stator disc, the other element being connected with the housing, and the servomotor being effective to shift the stator disc so as to decrease the width of said gap under the action of pressure in the first working space and to increase the width of said gap under the action of pressure in the second working space, the improvement comprising a reciprocable stop piston located in the cylinder element and defining therewith a sealed control chamber, the stop piston having one end surface which faces the second working space and is arranged to abut the servomotor piston element, and an opposite end surface which faces the control chamber; and transfer passage means through which liquid is introduced into and withdrawn from the control chamber.
 2. A grinding device as defined in claim 1 in which said one element of the servomotor is connected with the stator disc through a cylindrical part which is coaxial with both the stator disc and the housing and projects from the housing through a central opening in a wall thereof.
 3. A grinding device as defined in claim 2 in which the servomotor is coaxial with said cylindrical part; the piston element is connected with the cylindrical part; and the cylinder element is connected with the housing.
 4. A grinding device as defined in claim 2 in which the servomotor is coaxial with said cylindrical part; the piston element is connected with the housing; and the cylinder element is connected with the cylindrical part.
 5. A grinding device as defined in claim 2 which includes a plurality of said servomotors arranged parallel with and spaced around the axis of the cylindrical part, each servomotor being provided with said stop piston, control chamber and transfer passage means, and said one element of each servomotor being connected with the cylindrical part.
 6. A grinding device as defined in claim 5 including a set of means for guiding the stator disc for said axial movement, each means of the set being coaxial with one of the servomotors and comprising a stationary member connected with the housing and cooperating moveable member which is connected with the cylindrical part through a common connection which also serves to join that part to said one element of the associated servomotor.
 7. A grinding device as defined in claim 6 in which the piston elements of the servomotors are connected with the housing and the cylinder elements are connected with the cylindrical part. 